It is known to provide a seat for an automobile with a headrest device for protecting the head of a seated person from an impact by a collision by moving forward and for supporting the head of the seated person when the seated person is moved backward by inertia upon receipt of a collision from rear of a vehicle (See Patent Document 1, for example, which is cited below).
This seat comprises a backrest frame provided with a side-frame portion, a headrest frame provided between the side-frame portions and having a headrest mounting portion, a headrest mounted on the headrest frame, and a rear member mounted on the headrest frame through a shaft and a link mechanism. When the body of a passenger is moved backward by an impact from the rear and acts on the rear member, the rear member is moved backward from a normal position. With this movement, the headrest moves forward so as to support the head and shoulders of the passenger.
The applicant has developed a seat for a vehicle provided with the headrest return prevention mechanism in order to ascertain the support. The headrest return prevention mechanism will be described below referring to the attached drawings.
FIG. 6 is an explanatory view illustrating a state where the headrest return prevention mechanism is mounted on an upper frame of a backrest frame, FIG. 7 is an explanatory view illustrating the headrest return prevention mechanism, FIGS. 8 to 11 are explanatory views showing the headrest return prevention mechanism from the side face, in which FIG. 8 is an explanatory view illustrating a normal position of a movable portion in the headrest return prevention mechanism, FIG. 9 is an explanatory view illustrating a state where the movable portions of the headrest return prevention mechanism is displaced rearward, FIG. 10 is an explanatory view illustrating a state where the movable portion of the headrest return prevention mechanism exceeds a dead point M, FIG. 11 is an explanatory view illustrating a state where return of a headrest mounting rod is prevented by the headrest return prevention mechanism.
FIG. 6 is an explanatory view illustrating an essential part of the backrest frame in an enlarged manner. As shown in this figure, this headrest return prevention mechanism 50 is mounted on the center part of an upper lateral frame of a backrest frame 60. A headrest mounting rod 61 to which a headrest, not shown, is fixed is disposed along an upper lateral frame of the backrest frame 60 so that it can move in an upper front direction by a link mechanism provided at both side portions of the backrest frame 60 at a rear collision.
The headrest return prevention mechanism 50 is, as shown in FIG. 7, provided with an engagement piece 51 as a movable portion having an abutting face 51a and a bent engagement face 51b, a bracket 52 mounted as a fixed portion on the backrest frame 60, a mounting shaft 53 pivotally inserting both the engagement piece 51 and the bracket 52 integrally, a push nut 56 fixing the mounting shaft 53, a return spring 54 wound around the mounting shaft 53, and an elastic contact spring 55 wound around the mounting shaft 53 in the direction opposite to the return spring 54.
At normal times, as shown in FIG. 8, the abutting face 51a of the engagement piece 51 abuts the front face of the headrest mounting rod 61 by being urged by the elastic contact spring 55. The position of this engagement piece 51 is called as a normal position.
On the other hand, at a rear collision, the headrest mounting rod 61 is moved forward and the headrest (not shown) mounted on the headrest mounting rod 61 is moved forward as shown in FIG. 9. At this time, as shown in FIG. 10, by inertia of the rear collision, the engagement piece 51 is rotated rearward around the mounting shaft 53 by its own weight of the engagement piece 51 and moved rearward from a dead point M shown in FIG. 9. After that, the head of the passenger is moved rearward by inertia, by which the headrest is pressed rearward and the headrest mounting rod 61 is moved rearward, but since the engagement piece 51 is located in the rear of the dead point M shown in FIG. 9, the lower face of the headrest mounting rod 61 is engaged with a bent engagement face 51b of the engagement piece 51 as shown in FIG. 11, and the headrest mounting rod 61 is prevented from moving further rearward. As a result, in a state where the headrest supports the head of the passenger, the return is prevented. This position of the engagement piece 51 is called a fixed position.
Once the lower face of the headrest mounting rod 61 is engaged with the bent engagement face 51b as above, the engagement piece 51 of the headrest return prevention mechanism 50 is fixed at the fixed position and the headrest mounting rod 61 abuts the engagement piece 51 and made immovable, and thus, the headrest does not return to the original position. Therefore, the headrest having been moved forward once by rearward movement of the head of the passenger does not return to the original position again but support of the head by the headrest can be made more secure.
The headrest return prevention mechanism 50 is urged by the return spring 54 provided at the mounting shaft 53 so that the engagement piece 51 returns to the normal position. Therefore, if the headrest mounting rod 61 is moved forward by some reason other than the rear collision, the inertia is sufficiently weaker than that at the rear collision, and the engagement piece 51 does not move to the rear of the dead point M in FIG. 9. Thus, the engagement piece 51 is moved forward by urging of the return spring 54 and automatically returned to the normal position shown in FIG. 8. Therefore, nonconformity that the headrest return prevention mechanism is operated by some cause other than the rear collision and return of the headrest is disturbed can be prevented.
Moreover, even if the headrest return prevention mechanism 50 is operated at the rear collision and the return of the headrest is prevented, when a passenger slightly pulls the headrest forward by a hand or the like and then, pushes the headrest rearward so as to move the headrest mounting rod 61 to the rear again, the position of the headrest can be returned to the normal position shown in FIG. 8 by urging of the return spring 54. Thus, the headrest return prevention state where return is prevented once can be canceled by the passenger himself.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 1998(H10)-138812